The purpose of this application is to apply cutting-edge, high spatial resolution structural and functional magnetic resonance imaging (MRI) techniques to delineate volumes and functional connectivity profiles of hippocampal and thalamic substructures and to evaluate how they are affected by alcohol use disorder (AUD). Relevance: Conventional MRI techniques reveal deficits in global volumes of hippocampus and thalamus in AUD. Measures of undifferentiated structures, however, may overlook dissociable cognitive functions of substructures of the hippocampus and the thalamus, which may be differentially affected by AUD. High resolution MRI techniques will identify imaging biomarkers with high selectivity for characterizing the heterogeneous effects of AUD on the brain. Approach: Newly developed, high spatial resolution MRI techniques will be used to estimate volumes and functional connectivity maps of substructures of the hippocampus and the thalamus. Specific Aim 1 will use high spatial resolution structural imaging of hippocampus and thalamus to test the hypothesis that substructural volumes of the hippocampus (specifically CA2-3 and CA4/DG) and thalamus (specifically MD) will be smaller in AUD than controls. Specific Aim 2 will use high spatial resolution functional imaging of hippocampus and thalamus to test the hypothesis that hippocampal (Sub) and thalamic (MD) substructures will preferentially connect to prefrontal cortex, with compromised connectivity strength of these circuits in AUD relative to controls. Specific Aim 3 will evaluate heterogeneity of alcohol effects on hippocampus and thalamus by measuring thiamine levels in blood to test the hypothesis that low thiamine levels preferentially affect thalamic (MD) substructural volumes, and connectivity strength of the mammillothalamic tract. Summary: The in vivo interrogation of hippocampal and thalamic substructures and circuitry with high spatial resolution MRI will provide fine-grained anatomy of the functional substrates compromised in AUD. Highly selective imaging biomarkers of AUD can be used in future studies for the evaluation and monitoring of the efficacy of compensatory behavioral strategies or pharmacological treatment. A more refined understanding of hippocampal and thalamic anatomy and connectivity can furthermore be used to develop cognitive tasks to disentangle thalamic from hippocampal component functions and to explicate contradictory reports based on analysis of whole-structure volumes.